With rapid development of communications technologies, a transmission time interval (TTI) of data needs to be shortened in a Long Term Evolution (LTE) system. In a current LTE system, duration of a subframe is 1 millisecond (ms), and each subframe is further divided into two 0.5-ms timeslots. For a normal cyclic prefix (normal CP), each timeslot includes seven orthogonal frequency division multiplexing (OFDM) symbols. For an extended cyclic prefix (extended CP), each timeslot includes six OFDM symbols. The OFDM symbol is abbreviated as a symbol below. In the current LTE system, a TTI is duration of a subframe, that is, 1 ms. With technology evolution, a short TTI that can be supported by data transmission may reach 1-timeslot duration or even 1-symbol duration. This poses a new requirement on a current data transmission mechanism.
In the LTE system, before receiving or sending service data, a terminal device needs to learn of downlink control information (DCI) configured by an evolved NodeB for the terminal device. The DCI is carried by using a physical downlink control channel (PDCCH).
A currently defined PDCCH such as a PDCCH defined in a release (Rel)-8 and an enhanced PDCCH (ePDCCH) defined in a Rel-11 is used to schedule a data packet whose TTI is 1 ms. Consequently, for a data packet whose TTI is less than 1 ms, the currently defined PDCCH cannot effectively work. By using the PDCCH defined in the Rel-8 as an example, the PDCCH is on the first symbol, the first two, the first three, or the first four symbols in a subframe. When a base station needs to re-configure scheduling information for the data packet after a fifth symbol in the subframe, this cannot be implemented on the PDCCH defined in the Rel-8. Therefore, for the data packet whose TTI is less than 1 ms, design of the current PDCCH needs to be improved to support communication of a short-TTI data packet.